The present invention relates to a light-sensitive mixture, which becomes soluble by exposure, comprising
(a) a 1,2-quinonediazide or a mixture of PA0 (b) a water-insoluble binder soluble in aqueous-alkaline solutions, PA0 (c) an organic compound forming an acid on exposure, and PA0 (d) a dyestuff. PA0 R.sup.1, R.sup.2, R.sup.3 and R.sup.4 are hydrogen atoms or halogen atoms or nitro groups, with not more than two of these groups being hydrogen atoms and at least one thereof being a nitro group, PA0 R.sup.5 and R.sup.6 are hydrogen atoms or 1,2-naphthoquinone-2-diazide-4-sulfonyloxy radicals, with R.sup.5 and R.sup.6 being always different from each other, and PA0 R.sup.7 and R.sup.8 are hydrogen atoms or lower alkyl radicals, and (d) a dyestuff comprising an azo dyestuff containing at least one nitro group in the molecule. PA0 (a) a 1,2-quinonediazide or a mixture of PA0 (b) a water-insoluble binder soluble in aqueous-alkaline solutions, PA0 (c) an organic compound forming an acid on exposure and PA0 (d) a dyestuff.
(a.sup.1) a compound forming an acid on exposure and PA1 (a.sup.2) a compound having at least one C--O--C bond cleavable by acid, PA1 (a.sup.1) a compound forming an acid on exposure and PA1 (a.sup.2) a compound having at least one C--O--C bond cleavable by acid, PA1 R.sup.1, R.sup.2, R.sup.3 and R.sup.4 are hydrogen atoms, halogen atoms or nitro groups, with not more than two of these radicals being hydrogen atoms and at least one thereof being a nitro group, PA1 R.sup.5 and R.sup.6 are hydrogen atoms or 1,2-naphthoquinone-2-diazide-4-sulfonyloxy radicals, with R.sup.5 and R.sup.6 being always different from each other, and PA1 R.sup.7 and R.sup.8 are hydrogen atoms or lower alkyl radicals.
After exposure, the mixture shows a clearly visible color contrast between exposed and unexposed areas.
Mixtures of the generic type indicated are preferably used for preparing planographic printing plates and photoresists, and such mixtures are known, for example, from U.S. Pat. No. 3,969,118. The mixtures described there contain as the dyestuff (d) a triphenylmethane, azine or anthraquinone dyestuff and as acid forming organic compound (c) a 1,2-naphthoquinone-2-diazide-4-sulfonyl halide. After image exposure they produce an image contrast which is clearly visible in daylight or in white artificial light. However, the image contrast is less pronounced, and in some cases inadequate under the yellow safety light customarily used when working with reprographic materials.
U.S. Pat. No. 3,929,488 describes corresponding mixtures which contain certain azo dyestuffs as the dyestuffs and diazonium salts of strong acids as the acid donors. These mixtures produce only a relatively slight visual contrast in normal light and in safety light.
U.S. Pat. No. 4,163,672 and British Pat. No. 2,005,855 describe similar mixtures which contain diazonium salts as the acid donors and azo, triphenylmethane, azine or anthraquinone dyestuffs as the dyestuffs. Their contrast is likewise frequently inadequate in yellow safety light.
U.S. Pat. No. 4,160,671 describes corresponding mixtures which contain trihalogenomethyl-s-triazines or trihalogenomethyl-2-pyrones as the acid donors and azine, triphenylmethane or anthraquinone dyestuffs as the dyestuffs. The properties of these mixtures are similar to those of the abovementioned mixtures.
British Pat. No. 2,038,810 describes mixtures which contain as acid donors 1,2-naphthoquinone-2-diazide-4-sulfonic acid esters or amides of phenols or aromatic amines, which have electron-attracting substituents in the benzene nucleus. Preferred substituents are halogen atoms and nitro groups. The dyestuffs mentioned include triphenylmethane dyestuffs and oil-soluble dyestuffs. These mixtures produce color contrasts which are better discernible under yellow light than those produced by some of the other mixtures mentioned above; however, contrast still does not meet all requirements.